How to Use a Fused Glass Casting Mold: Prep, Fill Weights & Firing Schedules

Casting with a mold is easier than you think. Fill it with the right amount of glass, fire it on the right schedule, and the mold does the heavy lifting. This guide covers everything you need for my 5" casting molds.

This guide applies to: Wreath, Heart, Bloom, Star, Bell, Tree, Snowflake (solid), Snowflake (with Hole), Maple Leaf, Maple Leaf with Hole.

Each mold has been fired to 1900°F during production and is compatible with COE 96 and Bullseye/COE 90 glass.

Step 1: Prep your mold

Wipe the mold with a damp cloth to remove any dust and let it dry. Prep with ZYP BN spray (aerosol preferred). For the first prep, apply 3–4 even coats, following the manufacturer's directions. Change the angle of your spray as you go to get good coverage, especially on the centre post. Better to have too much than too little. Let each coat dry thoroughly, and reapply as needed.

Step 2: Weigh your glass

• Tack fuse: 85–100 g
• Full fuse: 100–120 g

Step 3: Build your piece

• 2–3 layers of ¼" pieces of glass work beautifully. Keep the pieces relatively flat.
• Avoid sharp points pressing into the mold walls. If glass points directly into the sidewalls or the inside shape, it can grip and make removal difficult.
• Take care placing glass at each point to enhance the inner shape.
• Add interest with medium frit, small cut pieces, or clear frit on top.
• Don't be afraid to fire a second time (outside of the mold) to add embellishments like murrini or frit for texture.
• Full fusing with frit only isn't recommended, because it's hard to reach the weight. If you must, load the frit in a peaked mound so the glass pushes down into the mold as it fuses.

Step 4: Fire it

No need to raise the molds; they have notches that allow for air flow.

Tack fuse (COE 96, side elements)

Full fuse (COE 96)

AFAP = as fast as possible.

Side vs. lid elements

If your kiln fires with lid elements, you may need to bring your top temperature down slightly for a tack fuse. Lid elements send directional heat, which can overfire the glass and leave you with more of a contour result. Fire a test sample first so you know your true tack fuse temperature.

A note on contour fusing

Contour temperatures are the riskiest for glass sticking to the middle of the mold. The glass isn't hot enough to flow, so it's more likely to grab.

Firing notes

• You may need small temperature adjustments depending on how full your mold is and how your kiln fires. Test your kiln to make sure you're getting a true tack fuse.

Bullseye / COE 90 users: swap in the appropriate tack or full fuse temperatures for your glass and anneal at 900°F.

Having trouble with release? Read why fused glass sticks to the mold, and how to fix it.

Show me what you make!

I would absolutely love to see what you create. Tag me @themichellefrost so I can cheer you on and share your work.

Warmly,
Michelle